Assembly substrates for overmolded devices such as ball grid arrays (BGAs) are highly variable in length, width, and thickness because of the imprecise and inexpensive manufacturing techniques used to create the assembly substrates. Conventional multiplunger mold presses can compensate for the thickness variation from one assembly substrate to another assembly substrate by using a movable insert in a cavity of a lower chase. However, the conventional multiplunger mold presses cannot compensate for the length or width variations of different assembly substrates. Therefore, after the assembly substrate is supported by the movable insert within the cavity of the lower chase, gaps are formed between the assembly substrate and sidewalls of the cavity. Consequently, during the molding process, a mold compound fills the gaps and often contacts the movable insert, which is located beneath the assembly substrate. After curing the mold compound, the insert is often locked in place by the hardened mold compound and is no longer movable. Consequently, the cost and cycle time for packaging a semiconductor device is increased because the lower chase must be cleaned prior to packaging another semiconductor device so that the mobility of the insert is restored and so that the insert can compensate for the different thickness of the next assembly substrate.
Accordingly, a need exists for a method of packaging semiconductor devices that is cost effective, that has an efficient cycle time, and that compensates for the variations in length and width of different assembly substrates.